TCP hole punching for Bitcoin nodes behind home NATs?

The examination of Network Address Translation (NAT) types across various environments and systems reveals a pattern in the deployment of EIM (Endpoint Independent Mapping) and A(P)DM (Address and Port-Dependent Mapping). In a test scenario involving multiple devices and networking setups, it is observed that EIM NATs are significantly more common compared to A(P)DM NATs.

In detail, devices such as an Office internet on Mac and a T-Mobile US hotspot consistently utilize EIM NATs for both IPv4 and IPv6 configurations. This consistency suggests a broader implementation of EIM NATs in environments where connectivity and network simplicity are prioritized. Conversely, the use of A(P)DM NATs is limited and appears in specific cases. For instance, a home router setup with OPNSense employs A(P)DM NAT for IPv4 but lacks IPv6 configuration altogether.

Challenges arise when Docker desktop applications attempt bridged networking over these NATs. For example, on a Mac using office internet, the Docker environment manages an APDM NAT for IPv4 but fails to establish a connection under IPv6. Similarly, Linux-based setups face connection failures when Docker utilizes bridged networking for both IPv4 and IPv6, indicating potential compatibility or configuration issues in more complex networking scenarios.

These findings underscore the prevalence of EIM NATs in most tested scenarios, providing robust connectivity solutions across different platforms and service providers. Meanwhile, the selective application and occasional connectivity issues with A(P)DM NATs highlight the need for careful consideration in network design and implementation, particularly when deploying containerized environments or configuring advanced network settings.